Lead plating method for GMR head manufacture

ABSTRACT

A major problem in Lead Overlay design for GMR structures is that the magnetic read track width is wider than the physical read track width. This is due to high interfacial resistance between the leads and the GMR layer which is an unavoidable side effect of prior art methods. The present invention uses electroplating preceded by a wet etch to fabricate the leads. This approach requires only a thin protection layer over the GMR layer to ensure that interface resistance is minimal. Using wet surface cleaning avoids sputtering defects and plating is compatible with this so the cleaned surface is preserved Only a single lithography step is needed to define the track since there is no re-deposition involved.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic disk storage withparticular reference to reading very high track densities

BACKGROUND OF THE INVENTION

The principle governing the operation of the read sensor in a magneticdisk storage device is the change of resistivity of certain materials inthe presence of a magnetic field (magneto-resistance).Magneto-resistance can be significantly increased by means of astructure known as a spin valve. The resulting increase (known as Giantmagneto-resistance or GMR) derives from the fact that electrons in amagnetized solid are subject to significantly less scattering by thelattice when their own magnetization vectors (due to spin) are parallel(as opposed to anti-parallel) to the direction of magnetization of thesolid as a whole.

The key elements of a spin valve structure are shown in FIG. 1. Seenthere, on substrate 10, is exchange pinning layer 7, made of PtMn orNiMn and having a thickness of about 100–300 Å. Layer 6 is a pinnedlayer of CoFe or CoFe/NiFe laminate, having a thickness of 20–200 Å.(for a synthetic spin valve the layer would be CoFe/Ru/CoFe). Layer 5 isa spacer layer of Cu, Au or Ag with a thickness of 5–25 Å while layer 4is the free layer, of CoFe or CoFe/NiFe laminate (thickness 20–200 Å).

Although layers 4–7 are all that is needed to produce the GMR effect,additional problems remain. In particular, there are certain noiseeffects associated with such a structure. As first shown by Barkhausenin 1919, magnetization in iron can be irregular because of reversiblebreaking of magnetic domain walls, leading to the phenomenon ofBarkhausen noise. The solution to this problem is to provide operatingconditions conducive to single-domain films for MR sensor and to ensurethat the domain configuration remains unperturbed after processing andfabrication steps. This is most commonly accomplished by giving thestructure a permanent longitudinal bias provided, in this instance, bylayer 3 which is a hard bias material such as Cr/CoPt or Cr/CoCrPt(where Cr is 0–200 Å), CoPt or CoCrPt (100–500 Å). Layer 2 is aprotection layer of Ta or Ru with a thickness of 1–30 Å.

Of particular interest for the present invention is layer 1 from whichthe input and output leads to the device are fabricated. An example of alead material is Ta/Au/Ta, where Ta is 20–100 Å and Au is 100–500 Å. Oneof the major problem in Lead Overlay (LOL) design is that the magneticread track width is wider than physical read track width. This is due tohigh interfacial resistance between the lead and the GMR layer ifintegration is done with conventional metallurgy. This is symbolized inFIG. 1 by current flow along path B instead of along the ideal path C.

In FIG. 2A we illustrate the first of two prior art methods that havebeen used to form the leads. With layers 3 through 7 in place, alift-off mask is formed. This comprises two layers 21 and 22. Bothlayers are light sensitive and therefore patternable in the usual way.Top layer 22 is conventional photoresist but lower layer 21 is amaterial that is readily etched away. Consequently, when a layer is laiddown over this structure, as shown in FIG. 2B, part of this layer (23A)deposits onto the spin valve top surface and part of it (23B) depositsonto upper pattern 22. Then when a solvent to remove part 21 is applied,the latter soon dissolves and part 22, including layer 23B, lifts offand is removed, leaving behind two leads separated by the original widthof 22, as shown in FIG. 2C.

The problem with this approach is that there is a degradation ofelectrical conductance at the tip of the lead arising from the resistshadowing leading to poor track width definition for extremely narrowtrack widths. Area “A” marked in FIG. 2C indicates the area of poortrack width definition and lowered electrical conductance area.

An improved fabrication process has been reported by Tanaka et al. andis illustrated in FIG. 3A. A dry etch is used to define the separationbetween the leads (track width 36). However, this approach also resultsin wider magnetic read width than physical read width because arelatively thick etch stop layer 32 is required in this approach toproperly define leads 33 without etching into the GMR sensor. This etchstop layer generally consists of slow dry etch materials such as Ta, Cr,W, Ti, or their alloys. These materials are often high in electricalresistivity and the resulting high interface resistance prevents theelectrical current from flowing into the very edge of the lead—thecurrent flow path that is obtained is the one marked as B in FIG. 3C.The ideal current flow path is marked by G in the FIG. 3C.

The present invention discloses a process to manufacture a structurethat allows current flow through path C, This results in much smallermagnetic/physical read track width difference.

A routine search of the prior art was performed with the followingreferences of interest being found:

In U.S. Pat. No. 6,188,495, Wiitala describes a lead process for a SVMR. In U.S. Pat. No. 6,118,621, Ohsawa also show a lead process. (Shoujiet al. discloses MR heads with different shaped leads in U.S. Pat. No.5,907,459 while in U.S. Pat. No. 5,761,013, Lee et al. discuss leads androuting.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a process for the formation of leads to a spinvalve structure.

Another object of at least one embodiment of the present invention hasbeen that said leads have a controlled gap less than about 0.15 microns.

Still another object of at least one embodiment of the present inventionhas been that said leads have minimal interface resistance to the deviceso that current flows into the device right before the gap, resulting ina precise magnetic (as opposed to physical) track width.

These objects have been achieved by using electroplating preceded by awet etch to fabricate the leads. This approach requires only a thinprotection layer over the GMR layer to ensure that interface resistanceis minimal. Using wet surface cleaning avoids sputtering defects andplating is compatible with this so the cleaned surface is preserved Onlya single lithography step is needed to define the track since there isno re-deposition involved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates why devices of the prior art exhibit greater magnetictrack widths than physical track widths.

FIGS. 2A–2C show a prior art process for forming the read gap, based onsputter deposition and liftoff.

FIGS. 3A–3C show a prior art process for forming the read gap, based onuse of an etch stop layer.

FIGS. 4A–4C illustrate the process of the present invention which isbased on use of electrodeposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process of the present invention starts as illustrated in FIG. 4A.Prior provision of a spin valve structure of the type discussed above isassumed. This includes layers 3 through 7 as shown in FIG. 4A.Additionally, there is a protective layer 41 on the top surfaces of bothlayers 3 and 4, which layers have been planarized so that their topmostsurfaces are coplanar. Layer 41 is typically about 1–30 Angstroms thickand is made of tantalum or ruthenium. Layer 41 will also serve as a seedlayer for the electroplating step that occurs later in the process.

A layer of a patternable resist material is then deposited ontoprotective layer 41. This resist material may be sensitive to eitherdeep ultraviolet (UV), which we will define here as radiation in thewavelength range of from 1,930 to 2,480 Angstroms or to electron beamradiation. The resist is deposited to a thickness between about 0.5 and1 microns. After exposure to (and development of) a suitable pattern ofthe selected radiation, a pedestal 42 of resist remains and is locatedmidway between the two biased layers 3, as illustrated in FIG. 4A.

Wet surface cleaning all of all exposed surfaces is now performed. Thisstep is highly dependent on the surface condition of the GMR sensor. Thegoal of this step is to remove organic contamination and reduce surfaceoxide so that uniform electroplating and minimal interface resistancecan be achieved. A typical 1–10% H₂:N₂ plasma ashing using 50–300 W forup to 60 seconds removes resist residue and organic contaminationwithout inducing further surface oxide formation.

An optional surface activation step may be introduced at this point. Forsurfaces that can be activated by acid, a brief dip in the platingsolution itself or in 1–10% HCl, H₂SO₄, or HNO₃ for 1–120 sec. issufficient to improve adhesion.

This is followed by a key feature of the invention, namely the layingdown of the lead layer. This is done by immersing the freshly cleanedprotective layer 41 in a plating solution, having a pH between about 1and 9, and then electroplating onto it metal layer 43, for between about1 and 120 seconds, as seen in FIG. 4B. The lead material of choicerequires low electrical resistivity (between about 2 and 10microohm-cm). The most commonly used is gold but other platable lowresistivity materials such as Cu, Ag, Ni, Co, Rh, Ir, Mo or their alloyscould also have been used. The thickness of this layer is between about100 and 1,000 Angstroms.

Gold plating can be done from commercial bright sulfite-based goldplating solution. Typical gold plating parameters are: Gold: 5–15 g/Land Sodium Sulfite: 45–55 g/L at a pH between 6.0–7.0. Plating isperformed in a temperature range of 15–80° C. at a current density of1–20 mA/cm², with 5 mA/cm² being preferred. Agitation level duringplating is mild.

Once electrodeposition has been completed (followed by rinsing indeionized water and blow drying), resist pedestal 42 is immediatelyremoved which results in the formation of a pair of leads 43, separatedby a gap 45, as seen in FIG. 4C. Gap 45 has a width between about 0.1and 0.5 microns. Removal of resist pedestal 42 was achieved by immersionin a solution of N-methyl 2-pyrrolidone at about 80° C.

The process concludes with the deposition of capping layer 46. A cappinglayer may be needed to improve adhesion of the lead material at the readgap. It can also reduce smearing during wafer lapping processes. Thechoice of capping layer includes Ta, W, Cr, TiW, and Ti. These materialshave good adhesion among layers and they are relatively high inelectrical resistivity. The thickness is up to 100 Angstroms. Commonsputter deposition is adequate for this application.

1. A process for forming leads to a magnetic read head, comprising:providing a spin valve structure having two opposing sloping sides oneach of which is a layer of longitudinally biased magnetic material,said biased material and said spin valve having coplanar topmostsurfaces on which is a protective layer; depositing a layer of a resistsensitive to deep UV on said protective layer; exposing said resistlayer to a deep UV pattern whereby, after development, a pedestal ofsaid resist remains midway between said biased layers; wet surfacecleaning all of said protective layer not covered by said pedestal;immersing said protective layer in a plating solution and thenelectroplating onto said protective layer a layer of a metal; removingsaid resist pedestal, thereby forming a pair of leads separated by agap; and depositing a capping layer on said pair of leads.
 2. Theprocess described in claim 1 wherein said UV sensitive resist isdeposited to a thickness between about 0.5 and 1 microns.
 3. The processdescribed in claim 1 wherein said plating solution is composed of: 5–15g/L of gold in an aqueous solution containing 45–55 g/L of sodiumsulfite.
 4. The process described in claim 1 wherein said gap has awidth between about 0.1 and 0.5 microns.
 5. The process described inclaim 1 further comprising performing said step of electroplating at acurrent density between about 1 and 20 mA/cm².
 6. The process describedin claim 1 wherein said electroplating step is performed for betweenabout 1 and 120 seconds whereby said metal layer has a thickness betweenabout 100 and 1,000 Angstroms.
 7. The process described in claim 1wherein said metal is selected from the group consisting of copper,silver, nickel, cobalt, rhodium, iridium, molybdenum, and their alloys.8. The process described in claim 1 wherein said metal has a resistivitybetween about 2 and 10 microohm-cm.
 9. The process described in claim 1wherein said electroplating step is performed at a temperature betweenabout 10 and 60° C.
 10. The process described in claim 1 wherein saidelectroplating solution has a pH between about 1 and
 9. 11. A processfor forming leads to a magnetic read head, comprising: providing a spinvalve structure having two opposing sloping sides on each of which is alayer of longitudinally biased magnetic material, said biased materialand said spin valve having coplanar topmost surfaces on which is aprotective layer; depositing a layer of a resist sensitive to anelectron beam on said topmost surfaces; exposing said resist layer to apattern mapped out by an electron beam whereby, after development, apedestal of said resist remains midway between said biased layers; wetsurface cleaning all of said protective layer not covered by saidpedestal; immersing said protective layer in a plating solution and thenelectroplating onto said protective layer a layer of a metal; removingsaid resist pedestal, thereby forming a pair of leads separated by agap; and depositing a capping layer on said pair of leads.
 12. Theprocess described in claim 11 wherein said UV sensitive resist isdeposited to a thickness between about 0.5 and 1 microns.
 13. Theprocess described in claim 11 wherein said plating solution is composedof: 5–15 g/L of gold in an aqueous solution containing 45–55 g/L ofsodium sulfite.
 14. The process described in claim 11 wherein said gaphas a width between about 0.1 and 0.5 microns.
 15. The process describedin claim 11 further comprising performing said step of electroplating ata current density between about 1 and 20 mA/cm².
 16. The processdescribed in claim 11 wherein said electroplating step is performed forbetween about 1 and 120 seconds whereby said metal layer has a thicknessbetween about 100 and 1,000 Angstroms.
 17. The process described inclaim 11 wherein said metal is selected from the group consisting ofcopper, silver, nickel, cobalt, rhodium, iridium, molybdenum, and theiralloys.
 18. The process described in claim 11 wherein said metal has aresistivity between about 2 and 10 microohm-cm.
 19. The processdescribed in claim 11 wherein said electroplating step is performed at atemperature between about 10 and 60° C. This is followed by a keyfeature of the invention, namely the laying down of the lead layer. Thisis done by immersing the freshly cleaned protective layer 41 in aplating solution and then electroplating onto it metal layer 43, as seenin FIG. 4B. The lead material of choice requires low electricalresistivity (between about 2 and 10 micr ohm-cm). The most commonly usedis gold but other platable low resistivity materials such as Cu, Ag, Ni,Co, Rh, Ir, Mo or their alloys could also have been used. The thicknessof this layer is up to 500 Angstroms.
 20. The process described in claim11 wherein said electroplating solution has a pH between about 1 and 9.